The present invention relates to heat exchangers and steam generators; and specifically to heat recovery steam generators.
A considerable amount of heat energy remains in the exhaust gases from many combustion processes. Several decades ago, this "waste heat" was allowed to escape through the smoke stack. With a heightened desire to conserve energy and make combustion systems more efficient, the waste heat now is frequently passed through a heat recovery steam generator (HRSG) to transfer much of the remaining heat from the exhaust gases to water that flows through the steam generator. The resulting steam can be used to generate electricity or used in equipment converts the energy in the steam into mechanical energy.
Typical HRSG systems comprise a large steel duct that channels hot gas over several banks of internal tubes which contain water. As the hot gases pass over the tubes, heat is absorbed by water flowing in the tubes. For maximum heat transfer, conventional systems are designed so that the tube banks are packed very densely into the duct. The dense configuration forces the hot gas to flow directly over the tube surfaces. The ends of the tube banks are in close proximity to the walls of the duct to eliminate passages above, below and on either side of the banks through which the hot gases could bypass the tubes. Designers of conventional HRSG systems often went to great lengths to plug even the smallest openings or cracks that might allow such bypassing to occur.
Although the dense tube configuration optimized the efficiency of previous HRSG systems, it made the systems very difficult to maintain. If the interior tubes of a bank needed repair, large portions of the system had to be disassembled in order to gain access to those tubes. This not only was very difficult but extremely time consuming, necessitating a long down time for the HRSG system. Even inspection of the inner tubes was difficult due to the dense configuration.
Therefore, it is desirable to provide a mechanism which allows relatively easy access to all of the tube panels within the HRSG system, while providing a very densely packed tube configuration for maximum operating efficiency.